The formation of aqueous slimes by microorganisms is a problem which is encountered in many systems. For example, the problem is not only found in natural waters such as lagoons, lakes, ponds, etc. and confined waters as in pools, but also in such industrial systems as cooling water systems, air washer systems and pulp and paper mill systems. All possess conditions which are conducive to the growth and reproduction of slime-forming microorganisms. In both once-through and recirculating cooling systems, for example, which employ large quantities of water as a cooling medium, the formation of slime by microorganisms is an extensive and constant problem.
Airborne organisms are readily entrained in the water from cooling towers and find this warm medium an ideal environment for growth and multiplication. Aerobic and heliotropic organisms flourish on the tower proper while other organisms colonize and grow in such areas as the tower sump and the piping and passages of the cooling system. The slime formation not only aids in the deterioration of the tower structure in the case of wooden towers, but also by its deposition on metal surfaces, promotes corrosion. In addition, slime carried through the cooling system plugs and fouls lines, valves, strainers, etc. and deposits on heat exchange surfaces. In the latter case, the impedance of heat transfer can greatly reduce the efficiency of the cooling system.
In pulp and paper mill systems, slime formed by microorganisms is commonly encountered causing fouling or plugging thereof. The slime also becomes entrained in the paper produced to cause breakouts on the paper machines with consequent work stoppages and the loss of production time and/or is responsible for unsightly blemishes in the final product which result in rejects and wasted output. The previously discussed problems have resulted in the extensive utilization of biocides in cooling water and pulp and paper mill systems. Materials which have enjoyed widespread use in such applications include chlorine, chlorinated phenols, organo-bromines, and various organo-surfur compounds. All of these compounds are generally useful for this purpose but each is attended by a variety of impediments. For example, chlorination is limited both by its specific toxicity for slime-forming organisms at economic levels and by the tendency of chlorine to react which results in the expenditure of the chlorine before its full biocidal function is achieved. Other biocides are attended by odor problems and hazards in respect to storage, use or handling which limit their utility. To date, no one compound or type of compound has achieved a clearly established predominance in respect to the applications discussed. Likewise, lagoons, ponds, lakes, and even pools, either used for pleasure purposes or used for industrial purposes for the disposal and storage of industrial wastes, become, during the warm weather, beseiged by slime due to microorganism growth and reproduction. In the case of the recreational areas the problem of infection is obvious. In the case of industrial storage or disposal of industrial materials, the microorganisms cause additional problems which must be eliminated prior to the materials use or the waste is treated for disposal.
Naturally, economy is a major consideration in respect to all of these biocides. Such economic considerations attach to both the cost of the biocide and the expense of its application. The cost performance index of any biocide is derived from the basic cost of the material, its effectiveness per unit of weight, the duration of its biocidal or biostatic effect in the system treated, and the ease and frequency of its addition to the system treated. To date, none of the commercially available biocides have exhibited a prolonged biocidal effect. Instead, their effectiveness is rapidly reduced as the result of exposure to physical conditions such as temperature, association with ingredients contained by the system toward which they exhibit an affinity or substantivity, etc., with a resultant restriction or elimination of their biocidal effectiveness.
As a consequence, the use of such biocides involves their continuous or frequent addition to systems to be treated and their addition to a plurality of points or zones in the systems to be treated. Accordingly, the cost of the biocide and the labor cost of such means of applying it are considerable. In other instances, the difficulty of access to the zone in which slime formation is experienced precludes the effective use of a biocide. For example, if in a particular system there is no access to an area at which slime formation occurs the biocide can only be applied at a point which is upstream in the flow system. However, the physical or chemical conditions, e.g., chemical reactivity, thermal degradation, etc. which exist between the point at which the biocide may be added to the system and the point at which its biocidal effect is desired render the effective use of a biocide impossible.
Similarly, in a system experiencing relatively slow flow, such as a paper mill, if a biocide is added at the beginning of the system, its biocidal effect may be completely dissipated before it has reached all of the points at which this effect is desired or required. As a consequence, the biocide must be added at a plurality of points, and even then a graduated biocidal effect will be experienced between one point of addition to the system and the next point downstream at which the biocides may be added. In addition to the increased cost of utilizing and maintaining plural feed points, gross ineconomies in respect to the cost of the biocide are experienced. Specifically, at each point of addition, an excess of the biocide is added to the system in order to compensate for that portion of the biocide which will be expended in reacting with other constituents present in the system or experience physical changes which impair its biocidal activity.
It is an object of the present invention to provide methods and compositions for controlling slime-forming microorganisms, in particular Aerobacter aerogenes in aqueous systems such as cooling water systems and pulp and paper mill systems, and for controlling slime formation or microorganism populations in aqueous bodies in general. Moreover, another object of the invention is the provision of methods and compositions for controlling slime-forming microorganisms in any aqueous system which is conducive to the growth and reproduction of Aerobacter aerogenes and, in particular, cooling water and paper and pulp mill systems. These systems employ a combination of 1,3-dichloroacetone oxime acetate and polyoxyethylene sorbitol hexaoleate having an average of 40 oxyethylene groups.
In practice of the invention, the combination is added to the particular system being treated, for example, cooling water systems, paper and pulp mill systems, pools, ponds, lagoons, lakes, etc. in a quantity adequate to control the slime-forming microorganisms and in particular Aerobacter aerogenes, which are contained by, or which may become entrained in, the system which is treated. It has been found that such compositions and methods control the growth and occurrence of such fungal, bacterial and algal microorganism as may populate these particular systems.
1,3-dichloroacetone oxime acetate, as disclosed in U.S. Pat. 3,733,419, is available commercially as Stauffer R-22938 (Stauffer Chemical Co.) and polyoxyethylene sorbitol hexaoleate having an average of 40 oxyethylene groups is also available commercially as Atlas G1086 or as POE-40 from Glyco Chemicals Inc.
As earlier stated, the inventive compositions are comprised of the latter compounds, either compound being present in such a quantity as to impart a synergistic behavior to the combination as a whole. The desirable weight ratio of the Stauffer R-22938 to the specific hexaoleate ranges from about 95:5 to about 5:95 with a range of 80:20 to 5:95 being a preferred range. When these two ingredients are mixed, the resulting mixtures possess a higher degree of slimicidal activity than the individual ingredients comprising the mixture. Accordingly, it is therefore possible to produce a more effective slime-control agent than the use of either ingredient alone. Because of the enhanced activity of the mixture, the total quantity of the biocide required for an effective treatment may be reduced. In addition, the high degree of biocidal effectiveness which is provided by each of the ingredients may be exploited without use of the higher concentrations of each.
To demonstrate the synergism which is provided by the inventive combinations of compounds, the data as set forth in the Table below was developed.